I use many at one time or another.
My primary option is WriteMonkey 3, which I used well before any shift to markdown. Looks simple, but is quite complex under the hood. Superb folding, but won’t interest many here because preview is just in a small side panel (I usually have it switched to other functions).
Some prefer to stick to the older version 2.7.
WM3 stores everything in a json database, but syncs that with linked files which is how I use it. 2.7 works only with files.
If I want WYSIWYG, I use Typora. Popular here and I know Silver is aiming at something similar for WYSIWYG here. Don’t especially like it myself.
I know some use VSCode with the Foam and Memo extensions. Probably OK if you usually have VSCode open. I’m not sure what extra functions they value over those in Obsidian.